1. Field of the Invention
The present invention relates to techniques for manufacturing data-storage media, such as compact discs (CDs) and digital video discs (DVDs).
2. Description of the Related Art
A conventional DVD player reads digital data stored on a DVD by illuminating the DVD with light from a laser and detecting and processing light reflected from different portions of the DVD (e.g., by rotating the DVD and moving the illuminating laser light radially). Portions of the DVD that store instances of the logical data value “1” have optical characteristics that are different from the optical characteristics of portions of the DVD that store instances of the logical data value “0”, such that the reflected laser light is different for logical “1”s and “0”s.
There are different ways to manufacture a DVD, including stamping and burning.
FIG. 1 shows a schematic cross-section of a portion of a conventional stamped DVD 100. Stamped DVD 100 comprises a plastic (e.g., polycarbonate) substrate 102 and a protective layer 106 with an intervening reflective (e.g., aluminum) coating 104. The interface between substrate 102 and protective layer 106 is defined by physical characteristics referred to as pits 108 and lands 110, which are distinguished by their different elevation levels in the Z direction represented in FIG. 1. As viewed in FIG. 1, lands correspond to plateaus (i.e., regions of relatively elevated elevation) in the topology of the upper surface of substrate 102, while pits corresponds to valleys (i.e., regions of relatively depressed elevation) in that topology. Depending on the DVD storage scheme, transitions between pits 108 and lands 110 may correspond to logical “1”s and “0”s.
According to one prior-art technique, substrate 102 is formed by physically pressing a heat-softened plastic disc (corresponding to substrate 102) against a master disc having “a mirrored image” of the pits and lands of substrate 102 to create pits and lands on the upper surface (as viewed in FIG. 1) of substrate 102. Reflective coating 104 is then applied (e.g., by sputtering or vapor deposition) to the upper surface of substrate 102, followed by application of protective layer 106 to form DVD 100 (e.g., by applying a spun coating of clear enamel). Note that protective layer 106 may also function as the label for stamped DVD 100. Stamped DVDs are typically manufactured in large quantities using sophisticated and expensive machinery.
An alternative to stamping DVDs is burning, where selected portions of a “blank” disc are illuminated with laser light that alters the optical characteristics of the disc material in those selected portions, thereby creating “optical” pits and lands that function analogously to the “topological” pits and land of a stamped DVD. One of the advantages of burning DVDs is that the technique can be implemented using equipment that is less expensive than the conventional machinery used to stamp DVDs. One of the disadvantages is that certain copyright protection schemes, such as the Contents Scramble System (CSS), are designed for stamped DVDs, but not for burnt DVDs.